1. Field of the Invention
The present invention relates to an imaging apparatus for an electronic endoscope for imaging an object in a body cavity, and an electronic endoscope having the imaging apparatus built-in.
2. Description of the Related Arts
Medical diagnoses using an electronic endoscope are widely performed. An imaging apparatus with an imaging device such as a CCD is built in a front end of an insertion section of the electronic endoscope, which is inserted into a body cavity. A processor device applies signal processing to an imaging signal obtained with the CCD, and an image in the body cavity can be observed on a monitor. Since a forceps channel through which a treatment tool is inserted is provided in the insertion section, biopsy in which affected tissue is removed with the treatment tool can be performed with observing the image in the body cavity.
As the imaging apparatus for the electronic endoscope, there is a type that uses a prism for guiding image light transmitted through an objective optical system to an imaging surface. In this type, the objective optical system for taking in the image light of the object in the body cavity is positioned at the front end of the insertion section of the electronic endoscope, and the CCD is arranged such that the imaging surface is parallel to an optical axis of the objective optical system. In regard to this type of imaging apparatus, dimension (thickness) in a direction vertical to the optical axis of the entire imaging apparatus including the objective optical system, the CCD, and the prism directly influences a diameter of the front end of the insertion section of the electronic endoscope. Therefore, various attempts have been made to narrow the diameter of the insertion section of the electronic endoscope by reducing the thickness of the entire imaging apparatus as possible (see Japanese Patents No. 2853939, 3364574, and 3186965).
The Patent No. 2853939 discloses a CCD package constituted of a bottom board and a reinforcement board. The bottom board includes an extended portion in a predetermined direction, and a CCD is placed on the surface thereof. The reinforcement board includes a containing hole to be placed on the surface of the bottom-base plate to form a containing portion of the CCD and an extended portion in a predetermined direction. The thickness of the bottom base plate is less than 0.5 mm. The extended portions of both the boards are overlapped to form the extended portion extending in one direction from one side of the boards. Terminals are provided on the extended portion. According to the CCD package, since the connecting pins protruding toward the bottom of a conventional package are not required, the signal lines can be wired by using an upper space of the extended portion, so that it is possible to reduce the entire thickness of the CCD package.
The Patent No. 3364574 discloses an imaging apparatus for the electronic endoscope in which the CCD package is not required. A conductor lead is formed by a TAB (Tape Automated Bonding) method in a terminal of the CCD so as to protrude from its outer circumference, and the CCD is provided in an opening hole of a circuit board to connect the conductor lead to a terminal of the circuit board.
The Patent No. 3186965 discloses a camera head device for the electronic endoscope. In the camera head device, an empty area where the terminals are not arranged is provided among the connecting terminal array on the CCD, and a supporting member of the objective optical system is attached to the empty area. According to the camera head device, since it is unnecessary to arrange the supporting member so as to avoid the bonding wires used for connecting the terminals, so that the diameter of the electronic endoscope can be narrow.
In the Japanese Patent Laid-Open Publication No. 2001-128937, the diameter of the insertion section is narrowed by devising the arrangement of the components in the insertion section. Signal cables, which are formed by bundling plural signal lines extending from an imaging device, are divided, and the signal cable having the largest outside diameter is closely arranged in a gap having the largest inside diameter of all gaps, which are formed between outer circumference of the incorporated object (forceps channel) having the largest outer circumference of all the incorporated objects and inner circumference of the insertion section. The outside diameters of the signal cable having the largest outside diameter and other signal cables are determined such that the inside diameter of the gap is the smallest at the time when these signal cables are arranged in the gap.
However, since the CCD is placed on the board in the Patent Nos. 2853939 and 3186965, the entire thickness becomes large. In addition, in the Patent No. 2853939, the plural boards having a special shape have to be used, and in the Patent No. 3186965, the layout of the terminals should be considered to provide the empty area. Therefore, there is a problem that the part cost is increased in both the cases.
In the Patent No. 3364574, since the CCD package is not required, the entire thickness is reduced in comparison with the above two cases. However, since the opening hole for arranging the CCD on the circuit board is required, there is also a problem that the part cost is increased.
In the Japanese Patent Laid-Open Publication No. 2001-128937, although the diameter of the insertion section is narrowed by dividing the signal cables, since the imaging device and the forceps channel which occupy the most of the area in the insertion section are not considered, the problem is not solved fundamentally.